The object of fiber-optic faceplate displays is to provide a reflective, i.e., passively illuminated, display device that appears brightly illuminated even in difficult viewing conditions, and with a pleasingly diffuse “paper-like” appearance.
Fiber-optic faceplate displays are described, for example, in U.S. Pat. No. 5,181,130, issued to Hubby, entitled “Fiber Optic Faceplate Liquid Crystal Display,” and U.S. Pat. No. 5,329,386, issued to Birecki and Hubby, entitled “Fiber-Optic Faceplate With Tilted Fibers.”
U.S. Pat. No. 5,181,130, which is incorporated herein by reference, discloses a liquid crystal display (LCD) that includes a layer of liquid crystal material, a fiber-optic faceplate, and one or more polarizers. The fiber-optic faceplate serves to allow ambient light from a much wider range of incident angles to illuminate the LCD, and allows the viewer to position himself so as to avoid front surface glare and still see the display brightly illuminated, even in difficult lighting situations.
FIG. 1 shows the fiber-optic faceplate LCD disclosed in U.S. Pat. No. 5,181,130. An incident illumination from a single direction will be spread into a hollow cone by the action of individual fibers of a fiber faceplate 119. Upon passage through a liquid crystal cell, the illumination may encounter a mirror 107 that sends the illumination back through the cell without depolarization or attendant loss in intensity. A second passage through the fiber faceplate 119 may result in a second azimuthal diffusion and the same hollow conical far field pattern.
Since the diffusions take place entirely before and entirely after the double passage of the light through the LC cell and polarizers 105(a), 105(b), there is no loss in light due to depolarization. In addition, the volume representing the intensity of light scattered at a given angle is an article of revolution about the normal to the display surface, not about the direction of specular reflection.
Thus, U.S. Pat. No. 5,181,130 discloses an LCD structure including a fiber-optic faceplate that does not degrade the viewing angle, contrast, or other operating features of the liquid crystal element itself, provides a wider angle over which ambient light is received for the purposes of illumination, and provides that the viewer need not be close to a position that would cause specularly reflected ambient light to fall in the viewer's eyes.
The LCD structure taught in U.S. Pat. No. 5,181,130 and other patents, however, proved difficult to build and disappointing in performance because of the requirement for polarizers 105(a), 105(b) that must be placed internal to the liquid crystal cell and withstand its subsequent processing, especially the high temperature cure of the polyamide alignment layers. The polarizers 105(a), 105(b) that are marginally suitable typically have poor transmission and low dichromic ratio, resulting in a dim display with poor contrast, thus defeating most of the potential advantages of the fiber-optic faceplate display.